Asymmetric synthesis of cyclic beta-hydroxyallylsilanes via sequential allyltitanation-ring closing metathesis

Highly enantioenriched cyclic beta-hydroxyallyisilanes have been prepared via enantioselective allylation of unsaturated aldehydes using a chiral allyltitanium reagent, followed by a ring-closing metathesis. Functionalized rings of various sizes have been synthesized and the electronic effect of the silicon group in the RCM reaction has been studied. The resulting cyclic beta-hydroxyallyisilanes reacted stereoselectively with a variety of electrophilic reagents. A first application of this method to the synthesis of a highly functionalized dihydropyrane is reported. (C) 2004 Elsevier Ltd. All rights reserved.